It is common practice to cool certain types of radiation detectors to cryogenic temperatures where high precision is required. Cooling of the detectors to a very low temperature reduces the effects of thermal noise on the detectors' output signals.
To maintain the detectors at both a relatively low and substantially constant temperature, the detectors are normally thermally isolated from the ambient environment by insulation. Moreover, a cooling agent, commonly liquid nitrogen, normally cools the detectors. However, other liquefied gasses may be used depending on the temperature at which the detectors should be maintained.
A known type of cryogenically cooled detector structure includes a Dewar in which inner and outer vessels forming the Dewar are cylindrical and are constructed of aluminum. The inner vessel is suspended from the top of the outer vessel by a short, thick, fiberglass-epoxy tube that is cemented at its junctions with the inner and outer vessels with epoxy resin. The tube provides thermal isolation between the inner and outer vessels, but permits liquid cooling agent to be manually poured into the inner vessel through a hole in the top of the outer vessel.
A detector may be mounted to the cylindrical outer surface of the inner vessel so that heat from the detector can be transferred directly to the relatively cool wall of the inner vessel. Radiation may be admitted to the detector through a window mounted in the cylindrical sidewall of the outer vessel. Typically, this window is held in place by a custom formed copper fitting and an elastomer o-ring engaged to the fitting to seal the space between the inner and outer vessels from the ambient atmosphere.
Cryogenically cooled detector structures that include Dewars that use liquid nitrogen or other cooling agents should be refilled with the cryogenic coolant on a periodic basis to replace liquid coolant that has evaporated over time. This is accomplished via a fill port integral with the detector structures. Conventionally, this refilling of the detector structures requires the manual intervention of an operator on a regular basis.